HID lamps as such are commonly known, so a description is kept brief here. Suffice it to say that such lamp comprises in most cases an elongate discharge vessel enclosing a discharge space with two electrodes and an ionizable gas filling. Alternatively the discharge vessel can be spherical shaped. During operation, a high voltage causes a discharge, resulting in a conductive plasma allowing a lamp current. As long as the current flows, the plasma is maintained. The amount of light generated depends on the current magnitude, and also the color may vary with current. Although it is possible to use direct current, it is common to use commutating direct current, i.e. the current magnitude remains constant but the direction is changed at a commutation frequency.
A particular group of HID lamps having widespread application in the fields of both public and domestic lighting comprise a ceramic discharge vessel. In this description and claims this means that the wall of the ceramic discharge vessel comprises a translucent crystalline metal oxide, like monocrystalline sapphire and densely sintered polycrystalline alumina (also known as PCA), YAG (yttrium aluminum garnet) and YOX (yttrium aluminium oxide), or translucent metal nitrides like AlN. The vessel wall may consist of one or more (sintered) parts, as known in the art.
HID lamps are favorable with a view to light output and energy consumption. However, an HID lamp cannot be powered directly from mains or any other voltage source, but requires an electronic driver. An HID system comprises the combination of the actual lamp and its electronic driver. An objective of the present invention is to provide a low-cost HID system. The cost price of the driver forms a major part of the cost price of the HID system. Thus, there is a demand for reducing the size and costs of the electronic driver.